Series de precipitación de la región centro oeste y sus variaciones

Se analizan las series de precipitaciones estivales de 8 estaciones meteorológicas de la región Centro Oeste de la Argentina mediante la aplicación de filtros de baja y alta frecuencias. Se establecen las matrices de correlación de las series originales y filtradas y se efectúa un análisis de enlace (linkage). Los resultados muestran que la región presenta igual variabilidad,1as ondas lar gas que la componen se encuentran en fase, con un período de 18 años aproximadamente por lo que están altamente correlacionadas. Las ondas cortas, más representativas del microclima de cada estación, no se correlacionan.The records of summer rainfall from 8 meteorological stations in the Central West region of Argentina has been analyzed by means of low-pass and high-pass filters. Linkage analysis has also been applied to the correlation matrix of filtered and unfiltered data. The results show that the region has equal variabllity, the long waves components are in face with a period of 18 years aproximately and high correlation coefficients. The short waves are more representatives of the microclima of each station. They are not correlated.Asociación Argentina de Geofísicos y Geodesta

Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century

South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia–New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisture transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions

Desarrollo de cronologías en el noroeste argentino

Se dan a conocer las cuatro primeras cronologías desarrolladas para el noroeste argentino. Dos de ellas han sido derivadas a partir de Cedrela angustifolia Sesse Moc. (cedro) y las dos restantes con Juglans australis (nogal). No existen antecedentes en el uso de estos dos géneros en estudios dendrocronológicos. Se analizan los parámetros estadísticos que caracterizan a cada una de las cronologías para orientar respecto a su uso potencial y a sus limitaciones. Se concluye que las cronologías obtenidas contienen una importante señal climática por lo que se recomienda su empleo en estudios paleoclimáticos y paleoecológicos.The first four chronologies developed for the argentine NO are stated. Two of them have been derived from Cedrela angustifolia Sesse Moc. (cedro) and the two left from Juglans australis (nogal). These genera are used for the first time in dendrochronological studies. There are analized statistic parameters characterizing each of the chronologies in order to determine its potential use and limitations. We conclude that the chronologies contain an important climatic sign, and this recommended its employment in palaeoclimatic and palaeoecologic studies.Asociación Argentina de Geofísicos y Geodesta

Fitzroya Cupressoides Yields 1534-Year Long South American Chronology

The longest tree-ring chronologies for the Southern Hemisphere published to date go back to A.D. 1011 in central Chile; 1028 in Tasmania, Australia; 1140 in western Argentina; and 1256 on the North Island, New Zealand. For paleoclimatic and other studies longer time series would be very desirable. Here we report on the first successful crossdating and chronology development for Fitzroya cupressoides, a redwood-like conifer in western Argentina, which goes back to 441 and exhibits desirable statistical characteristics.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Dendroclimatic Research in the South American Sector of the Southern Ocean: Indicators of Atmosphere-Ocean Climate Variability

A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term climatic variability at higher latitudes in the South American sector of the Southern Ocean. Based on the longest pressure records available in the South American-Antarctic Peninsula (SAAP) sector of the Southern Oceans, zonal and meridional indices have been developed for the region. Temperature records in southern South America and the Antarctic Peninsula are strongly affected by the strength of the meridional flow, whereas precipitation variations along the Pacific coast in southern South America are more related to changes in the zonal circulation at higher latitudes. We employed dendroclimatic techniques for reconstructing both the zonal (ZSAAP) and the meridional (MSAAP) circulation indices over the past four centuries. The ZSAAP reconstruction shows dominant modes of variation at around 4.4 and 5 years, which may be associated with the proposed Antarctic Circumpolar Wave in the Southern Oceans. Contrasting patterns in meridionality during the past two centuries are observed in the MSAAP reconstruction. Since the mid 1950s the northerly flow has steady increased, reaching unprecedented levels during the 1980s in the context of the past 400 years.Latin American Studie

Long-term glacier variations in the Central Andes of Argentina and Chile, inferred from historical records and tree-ring reconstructed precipitation

Snow and ice in the Central Andes of Chile and Argentina (33–36 °S) are the major source of water for the highly populated regions near the cities of Santiago and Mendoza. However, our knowledge of the forces driving the general glacier retreat in the region is limited. In order to obtain a long-term perspective of glacier fluctuations and their relationships with climate in the Central Andes, historical glacier variations were documented and compared with a tree-ring precipitation reconstruction based upon Austrocedrus chilensis trees. A multi-proxy approach (historical documents, old aerial photographs and satellite imagery) was used to map the fluctuations of eight glaciers, including the Cipreses Glacier, which provides the oldest record of glacier variations in the region starting in AD 1842. All the studied glaciers exhibited a negative trend during the 20th century with mean frontal retreats between - 50 and - 9 m y- 1, thinning rates between 0.76 and 0.56 m y- 1 and a mean ice area reduction of 3% since 1955. More than 350 tree-ring cores were combined into three tree-ring chronologies, which strongly correlate with the instrumental precipitation in Santiago de Chile (33°26' S; 70°41' W, 520 m asl). Based on these records, a 712-year precipitation reconstruction was developed. This reconstruction is characterised by a centennial oscillation indicating marked dry conditions around the years 1440 and 1600 AD. Wet conditions were prevalent in the years 1500, 1650 and particularly around 1850 AD. Since this precipitation maximum, the reconstruction shows a clear, secular, decreasing trend. The reduction in precipitation indicated by this reconstruction for the last 150 yr, in combination with a significant warming recorded in Central Chile, are the main causes of the observed current glacier retreats

Age effects on the climatic signal in <i>Araucaria araucana</i> from xeric sites in Patagonia, Argentina

<div><p><b><i>Background:</i></b> At different cambial ages, trees experience changes in their structure and interactions with environmental conditions. Reciprocal mechanisms between tree age and physical resources, photosynthetic rates, and xylem production may influence hydraulic resistance and plant water stress. However, it is yet uncertain how these mechanisms are associated with changes in growth sensitivity to biophysical drivers, especially climate.</p><p><b><i>Aim:</i></b> To establish age-associated climate – growth relationships in growth rings of <i>Araucaria araucana</i> trees from the temperate xeric zones of northern Patagonia, Argentina.</p><p><b><i>Methods:</i></b> We analysed the growth in 211 <i>A. araucana</i> trees from four sampling sites, in three age classes: young (≤120 years), mature (121–275 years), and old (≥276 years). We explored the correlations between the signal strength of tree growth and climate, based on comparisons between each age-class chronology and monthly mean surface air temperature, total precipitation, and the Southern Annular Mode (SAM) index.</p><p><b><i>Results:</i></b> The young trees showed higher correlations when their growth was compared with precipitation, air temperature, and the SAM index during austral spring and summer months of the same year. In contrast, growth in mature and old trees showed higher correlations with summer temperatures of the previous growing season.</p><p><b><i>Conclusions:</i></b> The sensitivity of the radial-growth response of <i>A. araucana</i> to climate varies with age and is strongest in the rings of young trees.</p></div

Climate variability 50,000 years ago in mid-latitude Chile as reconstructed from tree rings

High-resolution proxies of past climate are essential for a better understanding of the climate system. Tree rings are routinely used to reconstruct Holocene climate variations at high temporal resolution, but only rarely have they offered insight into climate variability during earlier periods. Fitzroya cupressoides - a South American conifer which attains ages up to 3,600 years - has been shown to record summer temperatures in northern Patagonia during the past few millennia. Here we report a floating 1,229-year chronology developed from subfossil stumps of E cupressoides in southern Chile that dates back to approximately 50,000 14C years before present. We use this chronology to calculate the spectral characteristics of climate variability in this time, which was probably an interstadial (relatively warm) period. Growth oscillations at periods of 150-250, 87-94, 45.5, 24.1, 17.8, 9.3 and 2.7-5.3 years are identified in the annual subfossil record. A comparison with the power spectra of chronologies derived from living F. cupressoides trees shows strong similarities with the 50,000-year-old chronology, indicating that similar growth forcing factors operated in this glacial interstadial phase as in the current interglacial conditions

Unusual Southern Hemisphere tree growth patterns induced by changes in the Southern Annular Mode

Recent changes in the summer climate of the Southern Hemisphere extra-tropics are primarily related to the dominance of the positive phase of the Southern Annular Mode. This shift in the behaviour of the Southern Annular Mode—essentially a measure of the pressure gradient between Southern Hemisphere mid and high latitudes—has been predominantly induced by polar stratospheric ozone depletion. The concomitant southward expansion of the dry subtropical belts could have consequences for forest growth. Here, we use tree-ring records from over 3,000 trees in South America, Tasmania and New Zealand to identify dominant patterns of tree growth in recent centuries. We show that the foremost patterns of growth between 1950 and 2000 differed significantly from those in the previous 250 years. Specifically, growth was higher than the long-term average in the subalpine forests of Tasmania and New Zealand, but lower in the dry-mesic forests of Patagonia. We further demonstrate that variations in the Southern Annular Mode can explain 12–48% of the tree growth anomalies in the latter half of the twentieth century. Tree-ring-based reconstructions of summer Southern Annular Mode indices suggest that the high frequency of the positive phase since the 1950s is unprecedented in the past 600 years. We propose that changes in the Southern Annular Mode have significantly altered tree growth patterns in the Southern Hemisphere